Silence uninitialized substr warning

Author: jakechirsch

pandas/_libs/src/vendored/numpy/datetime/np_datetime_strings.c

@@ -114,11 +114,11 @@ int parse_iso_8601_datetime(const char *str, int len, int want_exc,
                             int format_len,
                             FormatRequirement format_requirement,
                             double threshold) {
+  const char *substr = NULL;
   if (len < 0 || format_len < 0)
     goto parse_error;
   int year_leap = 0;
   int i, numdigits;
-  const char *substr = NULL;
   int sublen;
   NPY_DATETIMEUNIT bestunit = NPY_FR_GENERIC;
   DatetimePartParseResult comparison;